diff --git a/vm/src/obj/objenumerate.rs b/vm/src/obj/objenumerate.rs
index 76452e56c..fb7ae7c71 100644
--- a/vm/src/obj/objenumerate.rs
+++ b/vm/src/obj/objenumerate.rs
@@ -4,18 +4,20 @@ use std::ops::AddAssign;
 use num_bigint::BigInt;
 use num_traits::Zero;
 
-use crate::function::PyFuncArgs;
-use crate::pyobject::{PyContext, PyObject, PyObjectRef, PyResult, PyValue, TypeProtocol};
+use crate::function::{OptionalArg, PyFuncArgs};
+use crate::pyobject::{PyContext, PyObjectRef, PyRef, PyResult, PyValue, TypeProtocol};
 use crate::vm::VirtualMachine;
 
-use super::objint;
+use super::objint::PyIntRef;
 use super::objiter;
+use super::objtype::PyClassRef;
 
 #[derive(Debug)]
 pub struct PyEnumerate {
     counter: RefCell<BigInt>,
     iterator: PyObjectRef,
 }
+type PyEnumerateRef = PyRef<PyEnumerate>;
 
 impl PyValue for PyEnumerate {
     fn class(vm: &mut VirtualMachine) -> PyObjectRef {
@@ -23,26 +25,23 @@ impl PyValue for PyEnumerate {
     }
 }
 
-fn enumerate_new(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
-    arg_check!(
-        vm,
-        args,
-        required = [(cls, Some(vm.ctx.type_type())), (iterable, None)],
-        optional = [(start, Some(vm.ctx.int_type()))]
-    );
-    let counter = if let Some(x) = start {
-        objint::get_value(x).clone()
-    } else {
-        BigInt::zero()
+fn enumerate_new(
+    cls: PyClassRef,
+    iterable: PyObjectRef,
+    start: OptionalArg<PyIntRef>,
+    vm: &mut VirtualMachine,
+) -> PyResult<PyEnumerateRef> {
+    let counter = match start {
+        OptionalArg::Present(start) => start.value.clone(),
+        OptionalArg::Missing => BigInt::zero(),
     };
-    let iterator = objiter::get_iter(vm, iterable)?;
-    Ok(PyObject::new(
-        PyEnumerate {
-            counter: RefCell::new(counter),
-            iterator,
-        },
-        cls.clone(),
-    ))
+
+    let iterator = objiter::get_iter(vm, &iterable)?;
+    PyEnumerate {
+        counter: RefCell::new(counter.clone()),
+        iterator,
+    }
+    .into_ref_with_type(vm, cls)
 }
 
 fn enumerate_next(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
diff --git a/vm/src/obj/objgenerator.rs b/vm/src/obj/objgenerator.rs
index 611b89150..2fe08c138 100644
--- a/vm/src/obj/objgenerator.rs
+++ b/vm/src/obj/objgenerator.rs
@@ -4,13 +4,14 @@
 
 use crate::frame::{ExecutionResult, Frame};
 use crate::function::PyFuncArgs;
-use crate::pyobject::{PyContext, PyObject, PyObjectRef, PyResult, PyValue, TypeProtocol};
+use crate::pyobject::{PyContext, PyObjectRef, PyRef, PyResult, PyValue, TypeProtocol};
 use crate::vm::VirtualMachine;
 
 #[derive(Debug)]
 pub struct PyGenerator {
     frame: PyObjectRef,
 }
+type PyGeneratorRef = PyRef<PyGenerator>;
 
 impl PyValue for PyGenerator {
     fn class(vm: &mut VirtualMachine) -> PyObjectRef {
@@ -37,11 +38,8 @@ pub fn init(context: &PyContext) {
     );
 }
 
-pub fn new_generator(vm: &mut VirtualMachine, frame: PyObjectRef) -> PyResult {
-    Ok(PyObject::new(
-        PyGenerator { frame },
-        vm.ctx.generator_type.clone(),
-    ))
+pub fn new_generator(frame: PyObjectRef, vm: &mut VirtualMachine) -> PyGeneratorRef {
+    PyGenerator { frame }.into_ref(vm)
 }
 
 fn generator_iter(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
diff --git a/vm/src/obj/objlist.rs b/vm/src/obj/objlist.rs
index 2780f7582..08d3ff2f4 100644
--- a/vm/src/obj/objlist.rs
+++ b/vm/src/obj/objlist.rs
@@ -119,14 +119,11 @@ impl PyListRef {
         )
     }
 
-    fn iter(self, vm: &mut VirtualMachine) -> PyObjectRef {
-        PyObject::new(
-            PyIteratorValue {
-                position: Cell::new(0),
-                iterated_obj: self.into_object(),
-            },
-            vm.ctx.iter_type(),
-        )
+    fn iter(self, _vm: &mut VirtualMachine) -> PyIteratorValue {
+        PyIteratorValue {
+            position: Cell::new(0),
+            iterated_obj: self.into_object(),
+        }
     }
 
     fn setitem(self, key: PyObjectRef, value: PyObjectRef, vm: &mut VirtualMachine) -> PyResult {
diff --git a/vm/src/obj/objmap.rs b/vm/src/obj/objmap.rs
index 2de5bc5ef..029d3bae9 100644
--- a/vm/src/obj/objmap.rs
+++ b/vm/src/obj/objmap.rs
@@ -1,14 +1,16 @@
-use crate::function::PyFuncArgs;
-use crate::pyobject::{PyContext, PyObject, PyObjectRef, PyResult, PyValue, TypeProtocol};
+use crate::function::{Args, PyFuncArgs};
+use crate::pyobject::{PyContext, PyObjectRef, PyRef, PyResult, PyValue, TypeProtocol};
 use crate::vm::VirtualMachine;
 
 use super::objiter;
+use super::objtype::PyClassRef;
 
 #[derive(Debug)]
 pub struct PyMap {
     mapper: PyObjectRef,
     iterators: Vec<PyObjectRef>,
 }
+type PyMapRef = PyRef<PyMap>;
 
 impl PyValue for PyMap {
     fn class(vm: &mut VirtualMachine) -> PyObjectRef {
@@ -16,26 +18,21 @@ impl PyValue for PyMap {
     }
 }
 
-fn map_new(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
-    no_kwargs!(vm, args);
-    let cls = &args.args[0];
-    if args.args.len() < 3 {
-        Err(vm.new_type_error("map() must have at least two arguments.".to_owned()))
-    } else {
-        let function = &args.args[1];
-        let iterables = &args.args[2..];
-        let iterators = iterables
-            .iter()
-            .map(|iterable| objiter::get_iter(vm, iterable))
-            .collect::<Result<Vec<_>, _>>()?;
-        Ok(PyObject::new(
-            PyMap {
-                mapper: function.clone(),
-                iterators,
-            },
-            cls.clone(),
-        ))
+fn map_new(
+    cls: PyClassRef,
+    function: PyObjectRef,
+    iterables: Args,
+    vm: &mut VirtualMachine,
+) -> PyResult<PyMapRef> {
+    let iterators = iterables
+        .into_iter()
+        .map(|iterable| objiter::get_iter(vm, &iterable))
+        .collect::<Result<Vec<_>, _>>()?;
+    PyMap {
+        mapper: function.clone(),
+        iterators,
     }
+    .into_ref_with_type(vm, cls.clone())
 }
 
 fn map_next(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
diff --git a/vm/src/obj/objset.rs b/vm/src/obj/objset.rs
index 7f54c0d65..2b4626146 100644
--- a/vm/src/obj/objset.rs
+++ b/vm/src/obj/objset.rs
@@ -7,21 +7,22 @@ use std::collections::{hash_map::DefaultHasher, HashMap};
 use std::fmt;
 use std::hash::{Hash, Hasher};
 
-use crate::function::PyFuncArgs;
+use crate::function::{OptionalArg, PyFuncArgs};
 use crate::pyobject::{
-    PyContext, PyIteratorValue, PyObject, PyObjectRef, PyResult, PyValue, TypeProtocol,
+    PyContext, PyIteratorValue, PyObjectRef, PyRef, PyResult, PyValue, TypeProtocol,
 };
 use crate::vm::{ReprGuard, VirtualMachine};
 
 use super::objbool;
 use super::objint;
 use super::objiter;
-use super::objtype;
+use super::objtype::{self, PyClassRef};
 
 #[derive(Default)]
 pub struct PySet {
     elements: RefCell<HashMap<u64, PyObjectRef>>,
 }
+pub type PySetRef = PyRef<PySet>;
 
 impl fmt::Debug for PySet {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
@@ -151,23 +152,20 @@ fn set_clear(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
 }
 
 /* Create a new object of sub-type of set */
-fn set_new(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
-    arg_check!(
-        vm,
-        args,
-        required = [(cls, None)],
-        optional = [(iterable, None)]
-    );
-
-    if !objtype::issubclass(cls, &vm.ctx.set_type()) {
+fn set_new(
+    cls: PyClassRef,
+    iterable: OptionalArg<PyObjectRef>,
+    vm: &mut VirtualMachine,
+) -> PyResult<PySetRef> {
+    if !objtype::issubclass(cls.as_object(), &vm.ctx.set_type()) {
         return Err(vm.new_type_error(format!("{} is not a subtype of set", cls)));
     }
 
     let elements: HashMap<u64, PyObjectRef> = match iterable {
-        None => HashMap::new(),
-        Some(iterable) => {
+        OptionalArg::Missing => HashMap::new(),
+        OptionalArg::Present(iterable) => {
             let mut elements = HashMap::new();
-            let iterator = objiter::get_iter(vm, iterable)?;
+            let iterator = objiter::get_iter(vm, &iterable)?;
             while let Ok(v) = vm.call_method(&iterator, "__next__", vec![]) {
                 insert_into_set(vm, &mut elements, &v)?;
             }
@@ -175,12 +173,10 @@ fn set_new(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
         }
     };
 
-    Ok(PyObject::new(
-        PySet {
-            elements: RefCell::new(elements),
-        },
-        cls.clone(),
-    ))
+    PySet {
+        elements: RefCell::new(elements),
+    }
+    .into_ref_with_type(vm, cls)
 }
 
 fn set_len(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
@@ -190,16 +186,12 @@ fn set_len(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
     Ok(vm.context().new_int(elements.len()))
 }
 
-fn set_copy(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
-    trace!("set.copy called with: {:?}", args);
-    arg_check!(vm, args, required = [(s, Some(vm.ctx.set_type()))]);
-    let elements = get_elements(s);
-    Ok(PyObject::new(
-        PySet {
-            elements: RefCell::new(elements),
-        },
-        vm.ctx.set_type(),
-    ))
+fn set_copy(obj: PySetRef, _vm: &mut VirtualMachine) -> PySet {
+    trace!("set.copy called with: {:?}", obj);
+    let elements = obj.elements.borrow().clone();
+    PySet {
+        elements: RefCell::new(elements),
+    }
 }
 
 fn set_repr(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
@@ -335,67 +327,47 @@ fn set_compare_inner(
     Ok(vm.new_bool(true))
 }
 
-fn set_union(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
-    arg_check!(
-        vm,
-        args,
-        required = [
-            (zelf, Some(vm.ctx.set_type())),
-            (other, Some(vm.ctx.set_type()))
-        ]
-    );
+fn set_union(zelf: PySetRef, other: PySetRef, _vm: &mut VirtualMachine) -> PySet {
+    let mut elements = zelf.elements.borrow().clone();
+    elements.extend(other.elements.borrow().clone());
 
-    let mut elements = get_elements(zelf).clone();
-    elements.extend(get_elements(other).clone());
-
-    Ok(PyObject::new(
-        PySet {
-            elements: RefCell::new(elements),
-        },
-        vm.ctx.set_type(),
-    ))
+    PySet {
+        elements: RefCell::new(elements),
+    }
 }
 
-fn set_intersection(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
-    set_combine_inner(vm, args, SetCombineOperation::Intersection)
+fn set_intersection(zelf: PySetRef, other: PySetRef, vm: &mut VirtualMachine) -> PyResult<PySet> {
+    set_combine_inner(zelf, other, vm, SetCombineOperation::Intersection)
 }
 
-fn set_difference(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
-    set_combine_inner(vm, args, SetCombineOperation::Difference)
+fn set_difference(zelf: PySetRef, other: PySetRef, vm: &mut VirtualMachine) -> PyResult<PySet> {
+    set_combine_inner(zelf, other, vm, SetCombineOperation::Difference)
 }
 
-fn set_symmetric_difference(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
-    arg_check!(
-        vm,
-        args,
-        required = [
-            (zelf, Some(vm.ctx.set_type())),
-            (other, Some(vm.ctx.set_type()))
-        ]
-    );
-
+fn set_symmetric_difference(
+    zelf: PySetRef,
+    other: PySetRef,
+    vm: &mut VirtualMachine,
+) -> PyResult<PySet> {
     let mut elements = HashMap::new();
 
-    for element in get_elements(zelf).iter() {
-        let value = vm.call_method(other, "__contains__", vec![element.1.clone()])?;
+    for element in zelf.elements.borrow().iter() {
+        let value = vm.call_method(other.as_object(), "__contains__", vec![element.1.clone()])?;
         if !objbool::get_value(&value) {
             elements.insert(element.0.clone(), element.1.clone());
         }
     }
 
-    for element in get_elements(other).iter() {
-        let value = vm.call_method(zelf, "__contains__", vec![element.1.clone()])?;
+    for element in other.elements.borrow().iter() {
+        let value = vm.call_method(zelf.as_object(), "__contains__", vec![element.1.clone()])?;
         if !objbool::get_value(&value) {
             elements.insert(element.0.clone(), element.1.clone());
         }
     }
 
-    Ok(PyObject::new(
-        PySet {
-            elements: RefCell::new(elements),
-        },
-        vm.ctx.set_type(),
-    ))
+    Ok(PySet {
+        elements: RefCell::new(elements),
+    })
 }
 
 enum SetCombineOperation {
@@ -404,23 +376,15 @@ enum SetCombineOperation {
 }
 
 fn set_combine_inner(
+    zelf: PySetRef,
+    other: PySetRef,
     vm: &mut VirtualMachine,
-    args: PyFuncArgs,
     op: SetCombineOperation,
-) -> PyResult {
-    arg_check!(
-        vm,
-        args,
-        required = [
-            (zelf, Some(vm.ctx.set_type())),
-            (other, Some(vm.ctx.set_type()))
-        ]
-    );
-
+) -> PyResult<PySet> {
     let mut elements = HashMap::new();
 
-    for element in get_elements(zelf).iter() {
-        let value = vm.call_method(other, "__contains__", vec![element.1.clone()])?;
+    for element in zelf.elements.borrow().iter() {
+        let value = vm.call_method(other.as_object(), "__contains__", vec![element.1.clone()])?;
         let should_add = match op {
             SetCombineOperation::Intersection => objbool::get_value(&value),
             SetCombineOperation::Difference => !objbool::get_value(&value),
@@ -430,12 +394,9 @@ fn set_combine_inner(
         }
     }
 
-    Ok(PyObject::new(
-        PySet {
-            elements: RefCell::new(elements),
-        },
-        vm.ctx.set_type(),
-    ))
+    Ok(PySet {
+        elements: RefCell::new(elements),
+    })
 }
 
 fn set_pop(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
@@ -557,20 +518,13 @@ fn set_ixor(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
     Ok(zelf.clone())
 }
 
-fn set_iter(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
-    arg_check!(vm, args, required = [(zelf, Some(vm.ctx.set_type()))]);
-
-    let items = get_elements(zelf).values().cloned().collect();
+fn set_iter(zelf: PySetRef, vm: &mut VirtualMachine) -> PyIteratorValue {
+    let items = zelf.elements.borrow().values().cloned().collect();
     let set_list = vm.ctx.new_list(items);
-    let iter_obj = PyObject::new(
-        PyIteratorValue {
-            position: Cell::new(0),
-            iterated_obj: set_list,
-        },
-        vm.ctx.iter_type(),
-    );
-
-    Ok(iter_obj)
+    PyIteratorValue {
+        position: Cell::new(0),
+        iterated_obj: set_list,
+    }
 }
 
 fn frozenset_repr(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
diff --git a/vm/src/obj/objtuple.rs b/vm/src/obj/objtuple.rs
index 212005fdf..11d6a3694 100644
--- a/vm/src/obj/objtuple.rs
+++ b/vm/src/obj/objtuple.rs
@@ -4,7 +4,7 @@ use std::hash::{Hash, Hasher};
 
 use crate::function::OptionalArg;
 use crate::pyobject::{
-    IdProtocol, PyContext, PyIteratorValue, PyObject, PyObjectRef, PyRef, PyResult, PyValue,
+    IdProtocol, PyContext, PyIteratorValue, PyObjectRef, PyRef, PyResult, PyValue,
 };
 use crate::vm::{ReprGuard, VirtualMachine};
 
@@ -13,7 +13,7 @@ use super::objint;
 use super::objsequence::{
     get_elements, get_item, seq_equal, seq_ge, seq_gt, seq_le, seq_lt, seq_mul,
 };
-use super::objtype;
+use super::objtype::{self, PyClassRef};
 
 #[derive(Default)]
 pub struct PyTuple {
@@ -132,14 +132,11 @@ impl PyTupleRef {
         Ok(hasher.finish())
     }
 
-    fn iter(self, vm: &mut VirtualMachine) -> PyObjectRef {
-        PyObject::new(
-            PyIteratorValue {
-                position: Cell::new(0),
-                iterated_obj: self.into_object(),
-            },
-            vm.ctx.iter_type(),
-        )
+    fn iter(self, _vm: &mut VirtualMachine) -> PyIteratorValue {
+        PyIteratorValue {
+            position: Cell::new(0),
+            iterated_obj: self.into_object(),
+        }
     }
 
     fn len(self, _vm: &mut VirtualMachine) -> usize {
@@ -207,10 +204,10 @@ impl PyTupleRef {
 }
 
 fn tuple_new(
-    cls: PyRef<objtype::PyClass>,
+    cls: PyClassRef,
     iterable: OptionalArg<PyObjectRef>,
     vm: &mut VirtualMachine,
-) -> PyResult {
+) -> PyResult<PyTupleRef> {
     if !objtype::issubclass(cls.as_object(), &vm.ctx.tuple_type()) {
         return Err(vm.new_type_error(format!("{} is not a subtype of tuple", cls)));
     }
@@ -221,7 +218,7 @@ fn tuple_new(
         vec![]
     };
 
-    Ok(PyObject::new(PyTuple::from(elements), cls.into_object()))
+    PyTuple::from(elements).into_ref_with_type(vm, cls)
 }
 
 #[rustfmt::skip] // to avoid line splitting
diff --git a/vm/src/vm.rs b/vm/src/vm.rs
index 49bc2f9e2..3b3799d0f 100644
--- a/vm/src/vm.rs
+++ b/vm/src/vm.rs
@@ -353,7 +353,7 @@ impl VirtualMachine {
 
         // If we have a generator, create a new generator
         if code_object.is_generator {
-            objgenerator::new_generator(self, frame)
+            Ok(objgenerator::new_generator(frame, self).into_object())
         } else {
             self.run_frame_full(frame)
         }